1. Field of the Invention
The present invention relates generally to an at-sea vessel berthing facility and, more particularly, to an at-sea vessel-capturing berthing facility incorporating apparatus for mitigating relative motion between the berthing facility and the vessel.
2. Description of the Prior Art
Presently, the United States military must rely on overseas operating bases located on foreign soil to maintain an effective presence throughout the world. As stated in an article by James R. Blaker entitled "U.S. Overseas Basing System Faces A Difficult Transition", Armed Forces Journal International, February, 1989, pages 65 through 67, continued access by the U.S. military to these overseas land bases is becoming increasingly costly from a monetary standpoint and politically more difficult to maintain.
Over the past three decades, there have been two broad categories of monetary costs associated with overseas land basing. One of these may be referred to as the "fixed" costs of basing-fixed in the sense that these costs are tied directly to the facilities and installations built and maintained at the bases. These fixed costs can vary greatly from base to base, depending on the local costs, the design of the facility and its environment. Although some fixed costs are paid for by the nation in which the base is located, the greatest portion of the fixed costs are provided for under the defense budget and are ultimately paid for by the U.S. taxpayer. It is apparent that as world-wide inflation increases, the cost to the U.S. taxpayer proportionately increases.
The other broad category of monetary costs associated with maintaining overseas land bases is referred to as "permit" costs which are paid to a foreign nation to obtain the privilege and authority to build, improve and maintain a U.S. military facility on the nations's territory. In 1990, U.S. overseas land base permit costs ran at approximately seven (7) billion dollars The U.S. government paid approximately five (5) billion of this total, and the remainder was contributed by the U.S. taxpayer. To appreciate how rapidly these permit costs are rising, consider that in 1975, permit costs ran at roughly two hundred (200) million dollars, and by 1980, had risen to one (1) billion dollars. As with the increases in the fixed costs of overseas land basing, the majority of the increases in permit costs has also borne by the U.S. taxpayer.
In addition to the increased financial costs associated with the continued maintenance of overseas land bases, it has also become increasingly more difficult to deal politically with some foreign nations regarding continued U.S. access to these land bases. One need only consider Spain's rejection of a U.S. F-16 squadron in the late 1980's and the continued diplomatic sparring with the Philippines over base access and access compensation to recognize the political difficulties associated with maintaining foreign land bases.
The continued financial and political difficulties associated with the maintenance of foreign land bases has caused both the government and the industrial sector to examine alternatives to the foreign land base approach. For example, numerous concepts have been presented for airfields located at sea and for large, rectangular shaped "super islands" which in effect operate as multi-use floating complexes measuring one mile or more on a side. It has been suggested that these super islands be used as a replacement for foreign land bases. It is envisioned that the design characteristics of the super island would allow either industrial or military use.
Although the super island approach has recently been investigated to eliminate the problems associated with foreign land bases, the concept of large floating structures that can be used for floating cities, airfields or manufacturing facilities is not new. A form of the concept dates at least to 1932 when it was seriously proposed that stable landing fields be built in the mid-Atlantic as refueling stations to extend the range of commercial aircraft. Until recently the required technology was not available to advance the super island from the concept stage. With new developments in modular floating platform technology, however, the super island may indeed become a reality in the near future.
Although the utilization of super islands would eliminate the financial and political difficulties presently experienced with the maintenance of foreign land bases, super islands as presently envisioned would present their own set of difficulties with both construction and maintenance. For example, feasible transportation of the large modules forming the island structure from their point of manufacture to a location in international waters off the coast of a foreign land is doubtful, as is the connection of these large modules in an open seaway with today's methodology. Another anticipated limitation to the use of a structure as large as a super island containing all basing functions is its vulnerability to hostile attack.
An alternative to the super island approach is the subject of the above cross-referenced U.S. patent application Ser. No. 07/788,625, entitled "Operating At Sea Island Station". This application teaches the use of a plurality of discrete, floating operating units or vessels which may either be towed, hauled or self-propelled into position on the open ocean to form an operating base.
However, it is apparent that if the plurality of discrete operating units are to function as a single, self-sustained operating base, one or more of the operating units must be accessible by supply ship or other similar vessel to allow cargo and other supplies required by the base and carried by the ship or vessel to be unloaded and stored if desired. In addition, at least some of the operating units must be accessible by ship or vessel in order to allow transfer of cargo stored on these operating units to the remainder of the operating units forming the base.
One of the concerns regarding access to an operating unit positioned on the open ocean by ships or other similar vessels is the relative motion between the operating unit and the vessel which will occur when the vessel is docked with the operating unit for purposes of on or off-loading supplies. It is well known that on the open ocean, the wind, waves and currents cause dissimilar motion responses in different vessels. This relative motion between the operating unit and the vessel in open ocean conditions rapidly becomes destructive with sea states in excess of 3.
Consequently, a need exists for an at-sea docking or berthing facility which is capable of capturing a vessel in order to mitigate wind, wave and current-induced relative motion between the berthing facility and the vessel to permit safe and efficient on or off-loading of cargo to or from the vessel, or to permit the vessel to be serviced at sea.